docs: def wait_all(jobs, timeout=None):
      """ Return when at all of the specified jobs have completed or timeout expires.
  
      Args:
        jobs: a Job or list of Jobs to wait on.
        timeout: a timeout in seconds to wait for. None (the default) means no timeout.
      Returns:
        A list of the jobs that have now completed or None if there were no jobs.
      """
      return Job._wait(jobs, timeout, concurrent.futures.ALL_COMPLETED)